Katalytisk förädling av koldioxid till metangas

Abstract

This study explores catalytic methanation of carbon dioxide as a part of CCU technologies to enable a carbon cycle. The aim of this project was to design, synthesise and evaluate catalysts containing palladium dispersed on a carrier consisting of cerium and zirconium (CexZr1−xO2). By varying the composition of the carrier material (0, 2.5, 5 and 10 wt% Zr) and the temperature of the calcina tion (400 °C and 600 °C) the influence of these factors on catalytic activity and selectivity was examined. The carrier materials were made through two rounds of co-precipitation, where revisions of the synthesis method were applied to maintain desirable pH and effective filtration of the sample. All carrier materials were characterized by X-ray diffraction, confirming the formation of a homogenous solid solution with zirconium successfully incorporated into the crystal structure of cerium oxide. Also, X-ray fluorescence showed that the compositions of the samples were within the desired range. Furthermore, gas adsorption was used to characterize the surface area highlighting the samples calcinated at 400°C to have a significantly larger surface area (up to 138 m2/g) compared to samples calcinated at 600 °C, following thermically induced sintering. Reactor trials were carried out between 150 °C and 350 °C, with hydrogen gas and carbon dioxi de diluted in argon in a flow reactor. The results displayed that the conversion of carbon dioxide increased with temperature to a maximum of 20 %, but that the selectivity of methane was very low. Instead the formation of carbon monoxide and water dominated, probably through the reverse water gas shift reaction. The high selectivity of carbon monoxide is believed to depend on a combination of a too low reaction temperature and a too high dispersion of palladium on the large surface areas, something that favours desorption of carbon monoxide over further hydrogenation to methane. The project’s conclusions are that future attempts should focus on increasing the calcination tempera ture of the carrier material to decrease the dispersion of the metal, and to enable a higher reaction temperature to favour the formation of methane.